1,849 research outputs found
Looking for a Rational Thermodynamics in the late XIX century
From Rudolf Clausiusâ classical version of Thermodynamics two different traditions of research really emerged. If James C. Maxwell and Ludwig Boltzmann pursued the integration of thermodynamics with the kinetic theory of gases, others relied on a macroscopic and more abstract approach, which set aside specific mechanical models. Starting from 1869, the French engineer François Massieu was able to demonstrate that thermodynamics could be based on two âcharacteristic functionsâ or potentials. Josiah W. Gibbs and Hermann von Helmholtz exploited the structural analogy between Mechanics and Thermodynamics: from a mathematical point of view, Helmholtzâs âfree energyâ was nothing else but Gibbâs first potential. In the meantime, in 1880, the young German physicist Max Planck aimed at filling the gap between thermodynamics and the theory of elasticity. Five years later Arthur von Oettingen put forward a formal theory, where mechanical work and fluxes of heat represented the starting point of a dual mathematical structure. In 1891 Pierre Duhem generalized the concept of âvirtual workâ under the action of âexternal actionsâ by taking into account both mechanical and thermal actions. Between 1892 and 1894 his design of a generalized Mechanics based on thermodynamics was further developed: ordinary mechanics was looked upon as a specific instance of a more general science
Characterizing the Hadley circulation response through regional climate feedbacks
The robust weakening of the tropical atmospheric circulation in projections of anthropogenic warming is associated with substantial changes in regional and global climate. The present study focuses on understanding the response of the annual-mean Hadley circulation from a perspective of interactions between climate feedbacks and tropical circulation. Simulations from an ensemble of coupled oceanâatmosphere models are used to quantify changes in Hadley cell strength in terms of feedbacks, radiative forcing, ocean heat uptake, atmospheric eddies, and gross moist stability. Climate feedbacks are calculated for the model integrations from phase 5 of CMIP (CMIP5) using radiative kernels. Tropical mean circulation is found to be reduced by up to 2.6% K^(â1) for an abrupt quadrupling of carbon dioxide concentration. The weakening is characterized by an increase in gross moist stability, by an increase in eddy heat flux, and by positive extratropical feedbacks, such as those associated with lapse rate and sea ice response. Understanding the impact of radiative feedbacks on the large-scale circulation provides a framework for constraining uncertainty in the dynamic climate response, including the hydrological cycle
Quantum limit in resonant vacuum tunneling transducers
We propose an electromechanical transducer based on a resonant-tunneling
configuration that, with respect to the standard tunneling transducers, allows
larger tunneling currents while using the same bias voltage. The increased
current leads to an increase of the shot noise and an increase of the momentum
noise which determine the quantum limit in the system under monitoring.
Experiments with micromachined masses at 4.2 K could show dominance of the
momentum noise over the Brownian noise, allowing observation of the
quantum-mechanical noise at the mesoscopic scale
Algebraic-matrix calculation of vibrational levels of triatomic molecules
We introduce an accurate and efficient algebraic technique for the
computation of the vibrational spectra of triatomic molecules, of both linear
and bent equilibrium geometry. The full three-dimensional potential energy
surface (PES), which can be based on entirely {\it ab initio} data, is
parameterized as a product Morse-cosine expansion, expressed in bond-angle
internal coordinates, and includes explicit interactions among the local modes.
We describe the stretching degrees of freedom in the framework of a Morse-type
expansion on a suitable algebraic basis, which provides exact analytical
expressions for the elements of a sparse Hamiltonian matrix. Likewise, we use a
cosine power expansion on a spherical harmonics basis for the bending degree of
freedom. The resulting matrix representation in the product space is very
sparse and vibrational levels and eigenfunctions can be obtained by efficient
diagonalization techniques. We apply this method to carbonyl sulfide OCS,
hydrogen cyanide HCN, water HO, and nitrogen dioxide NO. When we base
our calculations on high-quality PESs tuned to the experimental data, the
computed spectra are in very good agreement with the observed band origins.Comment: 11 pages, 2 figures, containg additional supporting information in
epaps.ps (results in tables, which are useful but not too important for the
paper
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